Background: As a group, patients with obstructive sleep apnea (OSA) are at increased risk of having automobile accidents. Previous studies using actual accident data have used only small numbers of subjects.
Objective: To determine the rate of automobile accidents in a large population of OSA patients using objective data from the Ministry of Transportation of Ontario (MTO).
Design: Retrospective study
Setting: Academic sleep disorders clinic and laboratory.
Participants: All cases of OSA polygraphically confirmed between June 1990 and June 1994.
Interventions: Cases of OSA were a priori divided into groups based on apnea-hypopnea index (AHI): (OSA1 - AHI 10-25, OSA2 - AHI 26-40, OSA3 - AHI>40) and driving records were obtained from the MTO. Age and sex matched controls were selected at random from drivers in the MTO driver database who hold passenger vehicle licences. Analysis was restricted to drivers with the same licence class.
Main outcome measures: Primary outcome measure was accidents in the five years preceding diagnosis. Secondary outcome was citations during the same period.
Results: There were 155 of 460 OSA patients with one or more accidents compared with 150 of 581 Controls for the same time period (x2=7.7,p<0.01). The rate of accidents/year, for the preceding five years, was 0.07+/-0.14 for Controls versus 0.09+/-0.14 for OSA (p <0.05). This difference could all be accounted for by increased accident rate in OSA patients with the highest AHI (OSA3) (MVA/yr: 0.11+/-0.15, 0.08+/-0.12, 0.06+/-0.14 for OSA groups 3,2,1 respectively) as there was no differences among Control, OSA1 and OSA2 accident rates. OSA patients had twice as many citations as Controls (1.74+/-2.13 vs 0.86+/-1.43 p<0.001) although the types of citation were the same.
Conclusions: Increased automobile accidents in OSA may be restricted to cases with more severe apnea (AHI >40). Despite the large sample size (an order of magnitude greater than previous reports using accident data) further study is needed with even larger numbers, including more measures of disease severity and rigorously controlling for driving exposure.